1. The Field of the Invention
The present invention generally relates to pluggable electrical or optical modules. More particularly, the present invention relates to cage systems that permit pluggable modules of different widths, such as optoelectronic transceiver modules, to be connected to electrical connectors on a host board.
2. The Relevant Technology
Fiber optics are increasingly used for transmitting voice and data signals. As a transmission medium, light provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Also, light signals are resistant to electromagnetic interferences that would otherwise interfere with electrical signals. Light also provides a more secure signal because it doesn't allow portions of the signal to escape from the fiber optic cable as can occur with electrical signals in wire-based systems. Light also can be conducted over greater distances without the signal loss typically associated with electrical signals on copper wire.
While optical communications provide a number of advantages, the use of light as a transmission medium presents a number of implementation challenges. In particular, the data carried by light signal must be converted to an electrical format when received by a device, such as a network switch. Conversely, when data is transmitted to the optical network, it must be converted from an electronic signal to a light signal. A number of protocols define the conversion of electrical signals to optical signals and transmission of those optical signals, including the ANSI Fibre Channel (FC) protocol. The FC protocol is typically implemented using a transceiver module at both ends of a fiber optic cable. Each transceiver module typically contains a laser transmitter circuit capable of converting electrical signals to optical signals, and an optical receiver capable of converting received optical signals back into electrical signals.
Typically, a transceiver module is electrically interfaced with a host device—such as a host computer, switching hub, network router, switch box, computer I/O and the like—via a compatible connection port. Moreover, in some applications it is desirable to miniaturize the physical size of the transceiver module to increase the port density, and therefore accommodate a higher number of network connections within a given physical space. In addition, in many applications, it is desirable for the module to be hot-pluggable, which permits the module to be inserted and removed from the host system without removing electrical power. To accomplish many of these objectives, international and industry standards have been adopted that define the physical size and shape of optical transceiver modules to insure compatibility between different manufacturers. For example, in 2000, a group of optical manufacturers developed a set of standards for optical transceiver modules called the Small Form-factor Pluggable (“SFP”) Transceiver MultiSource Agreement (“MSA”), incorporated herein by reference. In addition to the details of the electrical interface, this standard defines the physical size and shape for the SFP transceiver modules, and the corresponding host port, so as to insure interoperability between different manufacturers' products. There have been several subsequent standards, and proposals for new standards, including the XFP MSA for 10 Gigabit per second modules using a serial electrical interface, that also define the form factors and connection standards for pluggable optoelectronic modules, such as the published draft version 0.92 (XFP MSA), incorporated herein by reference.
While such standardization efforts provide a number of benefits, including interoperability, high port density, and the like, the standardization on a small form factor device has also resulted in a number of problems. In particular, there is a tradeoff between the desired to maximize the port density, and the need for a form factor large enough to support longer distance fiber optic links.
For example, the proposed physical dimensions of the XFP optoelectronic modules allow for electronic and optical capabilities that provide for transmission distances of approximately 10–20 kilometers. Such transmit distances are typically suitable to transmit data between computers in typically sized local area networks (LANs), storage area networks (SANs), and metropolitan area networks (MANs). However, there is a desire to support greater transmission distances—for example, on the order of 40 to 80 kilometers. Unfortunately, the physical size of the proposed standard modules may limit the ability to meet this objective.
In particular, one factor that limits the distance that an optoelectronic module can transmit a signal is the total power consumption of the module. For example, greater distances may require cooled laser systems, which come at a significant power penalty. However, standards (e.g., the proposed XFP MSA standard) define the physical size of the modules and the available power through the module connector in a manner that may preclude the ability to provide a transmitter that can achieve the greater transmission distances. For example, a module that uses a connector according to the standard has the ability to access at most about 6.5 W, which is divided among three supply voltages and thus may not be completely available for a given design. Consequently, there may be an inability to provide greater transmission distances with existing standard module sizes due to power limitations.
The ability to provide transceivers having greater power requirements is limited in other ways as well. In particular, higher power devices release greater amounts of heat, which must be continuously removed to ensure proper performance or to prevent damage to the device. Again, this is more difficult to do in small form-factor devices. Generally speaking, the ability to remove a given amount of power from a device is tightly coupled to the physical size of that device. Thus, it is relatively more difficult to remove a given amount of power from a smaller device than from a larger one.
While one solution to some of the above problems would be the development of a module having a larger physical form factor, this approach has drawbacks as well. In particular, the larger physical module would be incompatible with existing cage designs used for existing module form factors. Cages are useful for providing structural support for the modules and to (facilitate the insertion and withdrawal of pluggable modules. In higher power designs, the cage usually also incorporates heat sinking features to remove heat from the module. However, conventional cages have a size that does not readily permit the development of newer, longer-distance transceivers, especially for those that will likely require a larger form factor than those that are currently defined according to these standards. Moreover, if cages were to be designed specifically for modules having a larger form factor, then they would in turn be incompatible with existing modules having smaller form factors.
Thus, there is a need in the art for a module, such as an optoelectronic transceiver module, that is able to provide longer transmission distances and/or transmission rates. Preferably, the module would be capable of accommodating electrical and optical components that permit for long distance transmissions. Further, the module design should permit for the satisfactory dissipation of heat so as to prevent damage to the device. In addition, it would be an advancement in the art if the module maintains a low profile, and allows for high port density configurations, and yet has a larger physical width than existing module standards such that it that permits greater flexibility in terms of the amount and types of electrical and optical components that it can accommodate. In addition, it would also be an advancement in the art to provide a card cage system that could be populated with modules having the larger physical width. Preferably, the card cage design would also be able to accommodate modules constructed in accordance with existing standards that have smaller widths. Such a card system should, in addition to providing sufficient structural support to modules, provide sufficient heat dissipation and EMI reduction.